PROJECT SUMMARY HPV/p16-positive head and neck squamous cell carcinoma (HNSCC) patients have higher overall survival (OS) rates than do HPV/p16-negative patients. The primary treatment of this cancer is radiotherapy (RT) either alone or in combination with chemotherapy and HPV positivity is known to render tumors more sensitive to RT. However, to date, the underlying mechanisms of this favorable phenomenon remain unknown. The proposed study is aimed at addressing this important question via in vitro studies of molecular mechanisms, in vivo tests of tumor response, and analyses of human tumor tissue. Our long-term objective is to identify the mechanisms that govern favorable prognosis in HPV/p16-positive OPSCC and use this information to improve treatment outcomes for all patients. To fulfill this goal, we have generated preliminary data identifying a novel mediator of radioresistance, TRIP12, which is inhibited by p16 expression leading to enhanced response to radiotherapy. The immediate goals of this application are reflected by three specific aims: i) establish the regulatory connection between p16 and TRIP12 and determine the role of TRIP12 in radiation sensitivity, ii) examine the downstream effects of TRIP12 signaling on radioresponse, and iii) verify that TRIP12 expression is a prognostic marker in HNSCC as well as a predictive marker for radiosensitizers that target this signaling pathway. We hope that by delineating the novel p16-TRIP12 signaling network we can provide valuable insight into the phenomenon of radioresistance as well as develop rationally targeted radiosensitizers for clinical use.